For several years a system has been manufactured and marketed for inducing and controlling the moisture content in the atmosphere within a residential dwelling of other building. And the basic principle employed in such systems in generally well known and commonly referred to as "humidification" with the apparatus that is used called a "humidifier" by the heating and air conditioning industry.
The value of proper humidity control, of course, is especially beneficial to personal comfort in areas which have long winters, where a prolonged heating period is necessary, and in dry climates, where dry air exsists. The medical profession has long recognized and endorsed the health value of controlled moisture content in the local environment and, accordingly, the perfection of means and methods for better control thereof are highly sought after.
The usual system consists of a water reservoir (which is best known as mounted in the plenum of a warm air furnace) with the water level controlled by a relatively simple float valve connected to a convenient water source. Partly immersed in the water reservoir is a motor driven drum of polyureathane material. This material is used mostly because it exhibits high capillary attraction and affords a large area of evaporation with the flow of warm air currents over the surface of the polyureathane drum as it is rotated in the water bath. The warm air currents, of course, in turn introduce moisture into the ducts of the forced air heating system.
To control or meter the desired moisture level, a humidity sensing device, known as a humidistat, is usually mounted in a main trunk line duct or else it is located in a central living room or area of a residence to sense an average condition. The humidistat being, as will be appreciated, the counterpart of the well known thermostat.
The electrical requirements for operation of the humidifier system is normally a low voltage source (24 V., A.C) obtained from a transformer connected to the residence 117-120 V., A.C. wiring system. And, to make the system operational requires that low voltage control lines be interconnected between the transformer, the humidistat and the humidifier drum actuating motor. But the routing of these lines was and is complicated and results in considerable expense; particularly when installation is to be in an existing building. Labor costs, in fact, often exceed the cost of the basic product. Consequently, a "wireless" remote control system which would mean comparatively low cost installation and greater flexibility of control would be most beneficial.
Suitable wireless control systems would seem to include the "carrier current" types, radio frequency control systems, and ultra sonic means and methods.
Of these, the ultra sonic types are relatively expensive and, in addition, they have certain serious limitations. For example, their range is generally limited to the immediate area or room where both the control and the receiver are located. And while this is acceptable for an expensive color television set, the control being operated by the observer within sight of the set, and the cost not disproportionate to that of the television set, it is not suitable for operational control of a humidifier system which is itself relatively inexpensive and which may be located clear across the length of a house from where the control itself is disposed, or desired.
The radio frequency systems, particularly the low power radiation types, are commonly known as used with model boats, cars and airplanes and for garage door operation. However, while the control-transmitters are relatively simple, the receiver must be of a high gain type and it's therefor comparatively expensive. Also, both the control and receiver would require an antenna for radiation and reception of the signal. And, while such short comings could be accomodated, the location of the receiver in the area of the furnace duct work, which would also provide electro-magnetic shielding, would greatly attenuate the incoming signal and any adaptation necessary would add appreciably to the overall expense of the system in this form.
The carrier current type therefor appears to be the most appropriate from a cost standpoint and in that it is not susceptable to external influence; such as radiated spurious frequencies or noise, since the signal is confined and retained within the building wiring where used. The main problem and requirement is in selecting a frequency sufficiently far removed from the A.C. line frequency, and without harmonic interference, to assure compatability. Although a higher frequency requires an increased cost in the transistor used, it has been found that suitable transistors for operation of the proposed system, when properly designed, appear feasible at about $1.00 each, which is most nominal.